The thesis here is that, despite the constant cries of "fascism" when talking about right-wing policies, the real heirs of fascism are those on the progressive left. Liberals will probably take offense to this, but those of us who have read The Road to Serfdom will respond with, "No duh." The book is chocked full of comparisons between (mostly) early Twentieth Century progressives' political aspirations and those of the Italian and German fascists of the same era. Their goals seem to overlap more times than not and, even when talking about militarism—a concept that we mostly associate with conservatives these days—he brings up example after example of progressives calling for violence to advance their goals.
Now, Goldberg makes it very clear that his point is not say that modern liberals are Nazis. His problem is that the word "fascist" gets thrown around too much without understanding what the fascists actually exemplified.
Liberals tend to get a pass when making fascist proclamations. Just this morning, the following was posted in my Facebook feed by one of my progressive friends:
Whereas they saw this as "refreshing," I was a little sickened by its metaphorical call to violence on behalf of political ideology. I commented on the fascistic nature of the quote and the response was that context matters. Sorry to be cynical, but I think in this case the context that mattered was that a democrat said this and not a republican.
Like his more recent Tyranny of Cliches, Liberal Fascism serves as a guidebook to pinpointing hypocrisy and the totalitarian impulses of progressives and, to a somewhat lesser extent, so-called compassionate conservatives.